Technical Abstract:
The chemical defense mechanism of corn involving the preformed antimicrobial cyclic hydroxamic acids, DIMBOA and DIBOA, is not effective against Gibberella fujikuroi mating population A (MP-A; =Fusarium moniliforme, syn. F. verticillioides, since intercellular hyphae continue to invade host tissue well beyond the early stage of infection. Such infections result in either seedling disease or symptomless endophytic colonization of the plant. While these compounds have wideranging antimicrobial activity, MP-A is very tolerant because of its ability to detoxify the cyclic hydroxamic acids. However, one strain was discovered to be sensitive to these compounds and forms the basis for our report on the genetic and physiological analyses of the detoxification process. Genetic analyses assessing segregation of tolerant and sensitive progeny indicated that two loci, Fdb1 and Fdb2, are involved in detoxification. In vitro physiological complementation assays resulted in detoxification of the related antimicrobial BOA and have suggested an unidentified intermediate compound is produced. Cloning of Fdb1+ by genetic complementation is underway. Cloning and targeted disruption of the native Fdb1+ allele in a detoxifying strain of MP-A will allow for stringent testing of hypotheses regarding the impact of antimicrobial detoxification on fungal virulence and/or fitness for endophytic growth.